This script will take text and embed it into a picture via tampering with pixel LSB values.

stego.rb

#!/usr/bin/ruby
require 'rubygems'
require 'RMagick'
prompt = '> '
puts "Image to embed (not overwritten):"
print prompt
image_file = gets.chomp
img = Magick::Image::read(image_file)[0]
width = img.columns
height = img.rows
list = img.dispatch(0, 0, width, height, "RGB")

def to_bin input
  binary = []
  array = input.split('')
  array.each do |c|
    binary << "%08b" % c.ord
  end
  binary
end

puts "Enter message to stegonographically hide inside #{image_file}:"
print prompt
text = gets.chomp
value = to_bin text
embed = value.join
puts embed

bin_array = []
list.map{|n| bin_array << n.to_s(2)}

count = 0
embed.split('').each do |b|
  pixel = bin_array[count]
  lsb = pixel[-1..-1]
  lsb = b if b != lsb
  new_pixel = pixel[0..-2]+lsb
  bin_array[count] = new_pixel # embed the pixel
  count += 1
end

new_arr = []
bin_array.map{|x| new_arr << x.to_i(2)}

new_img = Magick::Image.constitute(width, height, 'RGB', new_arr)

puts "Pixel Binary LSB conversions done!"
puts "Save Pixel Binary to Image:"
print prompt
out_file = gets.chomp
new_img.write out_file